1. Field of the Invention
The field of the invention is that of joint closure boxes for optical cables, also known as splice organizers.
In a known way, a joint closure box for optical fiber cables has to fulfil several functions. It should:
provide for the stopping and mechanical holding of the constituent elements of the joined or connected optical fiber cables, notably the central strength element, the grooved core or the tube, the peripheral braid or rod reinforcements as well as the external sealing sheath; PA0 provide for the stable and shielded housing of the fiber joints or connections as well as the reserve lengths of optical fibers on the specific supports (generally called cartridges). Reserve lengths are provided to enable subsequent cable resplicing operations. The housing function should naturally meet the constraints that ensure the efficient working of the fibers, notably the constraints of imperviousness to weather vagaries and of minimal radius of curvature of the fiber windings; PA0 enable the fastening and stable holding of the supports and cartridges; PA0 provide a space for storing fiber transfer sections extending between the cable ends, on the one hand, and the supports or cartridges, on the other hand, within a shielded volume; PA0 enable the handling of the connections or joints and the fibers, during the first assembly as well as during subsequent reservicing operations, in doing so without hampering the working of the neighboring links.
2. Description of the Prior Art
There already exist known joint closure boxes fulfilling at least some of these functions to varying degrees.
These known devices can be classified according to the type of cable to which they apply. For, a distinction is made between two types of optical fiber cables, depending on whether the fibers are maintained around the central strength element of the cable by a grooved core (with helical or alternating pitch), or by guiding tubes.
In the field of joint closure boxes for cables with reinforcing tubes, there is a known device formed by cartridges in the form of hollowed disks receiving the connections or joints and reserve lengths of fibers at their center. These disks are stored juxtaposedly and coaxially, and can be extracted freely and separately from their stored position to provide for assembly and maintenance. This known system has the drawbacks generic to all the existing joint closure boxes. Thus, it gives no solution suited to all the types of cables, but a solution suited only to cables with tubes. No original mechanical stopping and holding structure is provided in the case of optical fibers with grooved core. Furthermore, the handling of the optical fibers makes it necessary to move aside the disk-shaped cartridges with all the risks and problems resulting therefrom for the fiber sections connected to these cartridges.
There is also a known optical fiber cable joining device including a plurality of substantially quadrangular cartridges, which can be arranged side by side in racks or, again, superimposed in the form of "drawers" as described in the European patent document 0 204 581. Another device of this type is described in the European patent document 0 222 691. This device stores reserve lengths in a cartridge which can take two positions, a closed position and an open position, enabling access to the reserve lengths. The opening of the cartridge leads to a major shifting of the optical fiber sections, with a great variation in their radius of curvature. This second type of known device is more particularly adapted to cables with tubes.
In the case of grooved core cables, this type of device has cable-spreader parts providing, firstly, for the stopping and holding of the cable elements and, secondly, for the separation into individual units of the optical fibers which then coil within the joint closure box towards the cartridges. These spreader parts are, for example, of the type described in the French patent document No. 2 585 139 or in the European patent document No. 0 225 986. These spreader heads are complicated and expensive parts that are relatively difficult to use (the spreader head of the above-mentioned patent 2 585 139 provides for the injection of the fibers into the head by compressed fluid). Furthermore, these approaches require a shielding of the fibers by tubing between the end of the core and the entry of the coiling and splicing cartridge. The tubing operation is made obligatory to shield the fibers because the handling of the cartridges makes it necessary to push them aside to a specific working zone for the connecting or maintenance operations.
Tubing is a highly penalizing constraint in terms of the costs of undertaking servicing operations on the joint closure boxes. It must be noted that a retubing operation is also necessary in the case of cables with tubular reinforcement: the tubes used in this type of cable generally have very poor thermal stability (expansion, relaxation and shrinkage) which may notably induce strains on the fibers if the radii of curvature are small, typically smaller than about 10 cm. Furthermore, the fact of not following precise and complicated operating procedures has proved to have serious consequences for the reliability of the product.
Finally, as a general rule, known joint closure systems provide only very low accessibility during maintenance.
The invention is aimed at providing a modular joint closure box for optical fiber cables that makes it possible, notably, to overcome these various drawbacks of existing systems.